The performance of the respiratory system is generally examined by pulmonary function tests (PFT), which are a broad range of tests that are usually done in a health care provider's office and at specialized facilities. The PFT characteristics are considered important and informative data for the respiration of a patient. However, its measurement has not yet been implemented in routine clinical practice because of the rather complicated apparatus required.
There are major categories of respiratory characteristics that may be obtained with pulmonary functional tests: 1) spirometric characteristics, 2) lung volumetric parameters, 3) airway resistance and 4) lung compliance.
Spirometric Characteristics.
In a spirometry test, a person breathes into a mouthpiece that is connected to a device called a spirometer. New generation spirometers are handheld, small, lightweight and fit into a general practitioner's office. Spirometers are either a volumetric type which measure the amount of air exhaled or inhaled within a certain time, as described, for example, in U.S. Pat. Nos. 4,944,306 and 4,324,260, or a flow type which measure how fast the air flows in or out from lungs, as described, for example, in U.S. Pat. Nos. 4,182,172; 4,638,812; 7,094,208 and 7,383,740.
Lung Volumetric Parameters.
Plethysmography is considered the “gold standard” for measuring lung volumes. A patient is situated in plethysmographs, also known as “body boxes” having a known volume and pants against a closed shutter to produce changes in the box pressure. Such devices are disclosed, for example, in U.S. Pat. Nos. 3,511,237 and 5,680,871. In addition to lung volume measurements, plethysmography allows estimating airway resistance, spirometry performance, and dynamic lung compliance (using a special subsystem). The main disadvantages of this equipment are high price, bulkiness, and difficulties with measurements in children, claustrophobic, and bed ridden patients, which cause inconvenience and limited accessibility.
U.S. Pat. No. 8,657,757 and U.S. Patent Application 2013/0190640, disclose devices and methods for measuring volumetric parameters, spirometric parameters, and lung compliance by deriving pulmonary volumes from flow rates without using a “body box”. The method includes measurement of a plurality of airflow rates and pressures within a chamber during interruptions of forced exhalation.
Airway Resistance.
The airway resistance refers to resistance in the respiratory tract to airflow. The airway resistance is defined as the ratio of driving pressure to the rate of air flow and is measured under dynamic conditions (when air is flowing). The resistance can change based on the health and conditions of the lungs. Most lung diseases increase airway resistance in many different ways. For example, in asthma attacks the bronchioles spasm increases resistance; emphysema also increases airway resistance because the lung tissue becomes too pliable; many lung infections increase a mucus production that also increasing the airway resistance. The airway resistance may be estimated by plethysmography that is considered as “gold standard”. Additional methods for airway resistance estimation are disclosed in U.S. Pat. Nos. 4,220,161; 5,233,998; 6,068,606 and U.S. Patent Application 2015/0057559.
Lung Compliance.
Lung compliance is defined as the volume change per unit of pressure change across the lung, and is an important indicator of lung health and function. Measurements of lung volumes differ at the same pressure between inhalation and exhalation, meaning that lung compliance differs between inhalation and exhalation.
Low compliance indicates stiff lungs and means extra work is required to bring in a normal volume of air. Disease states resulting in low compliance include the Adult Respiratory Distress Syndrome (ARDS), pulmonary edema, pneumonectomy, pleural effusion, pulmonary fibrosis, and pneumonia among others. Emphysema is a typical cause of increased lung compliance. Lung compliance varies with the size of the lungs; a child has a smaller compliance than an adult does.
The lung compliance may be estimated by the formula detailed in Nikischin et al. (1998), Am. J. Respir. Crit. Med., Vol. 158, pp. 1052-1060.
Additional methods for lung compliance estimation are disclosed in U.S. Pat. No. 6,068,602 and U.S. Patent Application 2016/0256073.
Diagnosis of Lung Diseases.
The main clinical roles of respiratory function tests include diagnosis, assessment of severity, monitoring treatment and evaluation of prognosis.
Spirometry is one the most useful diagnostic tests, which measures vital capacity and force expiratory volume in 1 second. These parameters permit differentiation between restrictive and obstructive respiratory diseases. The spirogram flow-volume curves are used for diagnosis, however, combined diseases are not always visible in such graphs as their single elements. Further tests, like diffusion or provocation testing, provide a physician with more information.
U.S. Pat. No. 5,984,872 describes a spirometer with special electronic module, which is electrically connected to a computer through an analogue to digital converter that allows calculating and evaluating an expiratory flow-volume curve shape for diagnostic analyses. U.S. Publication No. 2011/0201958 discloses a hand-held device for determining at least one pulmonary function, designed to minimize measured air displacement due to shuttering. U.S. Pat. No. 5,634,471 discloses a flowmeter for measuring peak expiratory flow. U.S. publication 2016/0038057 discloses an airflow perturbation device for measuring respiratory resistance, compliance, and inertance. International application, Publication No. WO 2016/185470, discloses a pulmonary function testing device for measuring air flow while a subject breathes through two or more air flow resistors, including computational analysis done in order to obtain the subjects' respiratory related parameters.
There is an unmet medical need for a device for pulmonary function tests, which is hand-held, portable, and inexpensive. The device should be sufficiently easy to use for patients themselves to perform home monitoring. It should not require extensive maintenance. The system should also be capable of interfacing with a computer or the internet to allow convenient data collection. In addition, such apparatus should be used under various conditions, including stress, and the like. In addition, it is very important to develop of the simple and effective methods to determination of the basic functional properties of the respiratory system. In addition, the proposed Spiro-Test System (STS) should be owned of acceptable accuracy and reliability, and its measurement process no effect on the natural condition of the lung.